a. Technical Field
The invention relates to a pneumatic transportation system for transferring a particulate material from a storage container to a receiving unit having a higher or a lower pressure. A system according to the invention is particularly intended for feeding particulate fuel from a storage container to a combustion chamber operating at a higher pressure. The invention can thus replace a conventional sluice or lock hopper system or similar feeding system. A transportation system according to the invention may be included in a power plant for feeding fuel, sulfur absorbent material and bed material into a fluidized bed contained in a pressurized combustion chamber, a so-called PFBC plant, in which the operating pressure in the combustion chamber may be up to about 2 MPa (20 bar). A transportation system according to the invention may also be used for extracting bed material or separated ashes in such a PFBC plant.
b. Prior Art
When transferring particulate material between regions at different pressure levels, a so-called lock hopper system is usually used, that is, two containers are arranged in series with a valve upstream of the first container, between the containers and downstream of the last container. For transferring material from a storage container under atmospheric pressure to a receiving unit under supraatmospheric pressure, material is transferred from the storage container to the first container, while it is under atmospheric pressure. The valve at the inlet is then shut and the first container is pressurized. The valve between the containers is next opened and the material is transferred to the second pressurized container; the valve between the containers is then shut; the valve downstream of the second container is opened and the second container is emptied, whereupon the downstream valve can be closed again. The first container can be relieved of pressure and the valve upstream of it opened to again allow material to transfer from the storage container to the first container. A lock hopper system gives a discontinuous flow, unless it is supplemented with a rotary feeder downstream of the second lock hopper container.
A report from the Argonne National Laboratory, of 9700 South Cass Avenue, Argonne, Ill. 6043, October 1982, entitled "Discharge and Handling of Solids from Pressurized Fluidized-Bed Combustors", written by John E. Hanway Jr. and W. F. Padolski, describes various lock hopper systems and fuel feeding systems.
The European Pat. No. 0 040 708 describes a transportation system with material feeders of sluice type.